It has been found desirable to minimize the amount of water in canned food products such as tuna fish.
In one commonly used process effecting such yield improvement, the tuna fish is treated with hydrolyzed casein. One common hydrolyzed casein so utilized comprises a precipitated casein subjected to a high pH such as a pH of 9 or more. The use of monovalent hydroxide, such as sodium and potassium hydroxide, is conventional where a clear liquid is desired.
Divalent hydroxide, such as calcium hydroxide, has also been used to hydrolyze the casein where a milky liquid is acceptable.
It has also been indicated in the prior art that simple sodium caseinate does not perform the desired function.
Such alkaline hydrolyzed caseins have not proven completely satisfactory. The high pH of the indicated process presents a serious physiological irritant and health hazard to the people who handle the material. The high pH also causes severed machine corrosion and wear, concrete floor corrosion, and the stripping of paint from associated processing machinery. It has also been found that the use of such highly caustic alkaline hydrolyzed casein may reduce the shelf life of the canned tuna by approximately one-half due to accelerated corrosion of the can and enamel liner. A caseinate alternative has been produced by subjection of the caseinate to enzymes which cleave bonds in the K-casein fraction. Unless calcium is present in the system precipitation does not occur, nothwithstanding the K-casein cleavage. In such precipitation, the destabilized casein micelle uptakes calcium so as to define a calcium cross-linked mass.
Solubilization of the enzyme precipitated casein is conventionally effected by exposure thereof to a high pH such as 9.0 or above.
Resolubilized enzyme precipitated casein exhibits a substantially higher viscosity than resolubilized acidified casein.
A wide variety of enzymes capable of effecting precipitation of casein from milk is known. These include chymosin (commonly referred to as calf rennet), pepsin, chymotrypsin, and microbial enzymes biochemically related to chymosin in their mode of action and specificity. Such microbial enzymes include, but are not limited to, enzymes from Mucor pusilis, Mucor meihi, and endothia parasitica. Conventional proteolytic enzymes for treating casein include pancreatin, bromelin, and various proteolytic fungal and bacterial enzymes.